Image enhancement processing for improving the image quality by sharpening an image has been widely known conventionally. For example, a conventional television receiver carries out outline compensation for sharp-rising and sharp-falling of a video signal corresponding to an outline portion of an image to be displayed. This contour compensation extracts a high frequency component of an input image signal (a luminance signal), amplifies the high frequency component, and then adds the amplified high frequency component to the input image signal, thereby improving visual quality. FIGS. 10(A)-10(C) are diagrams illustrating changes in a waveform of the signal level of the image caused by the conventional image enhancement processing. FIG. 10(A) is a diagram illustrating a horizontal direction waveform of a signal level of the input image signal particularly illustrating a waveform of a portion corresponding to an edge where the signal level changes in the horizontal direction. FIG. 10(B) illustrates the high frequency component extracted from the input image signal. By amplifying the high frequency component and adding the amplified high frequency component to the input image signal, an output image signal having a sharp rising edge as illustrated in FIG. 10(C) may be obtained.
In recent years, also, there has also been suggested a technique called super-resolution that particularly up-converts the input image into an output image of higher resolution and carries out the image enhancement processing on an image obtained by the up-conversion (for example, see Non-Patent Document 1).